Update to beta 8 and update demo .gdextension.

[cridenour]

https://github.com/godotengine/godot/pull/67906 updates how gdextension libraries are expected to be named. I tried the new autodetect_library_prefix but it's broken at the moment (loads fine in editor, won't load in export).

[2shady4u]

Thank you for the update 😄